The present disclosure relates to an electronic device having a touch panel and a coordinate detection method used in the electronic device.
As widely known, a touch panel is configured by combining a display device such as a liquid crystal panel and a touch pad (position input device).
The touch panel includes a capacitive touch panel that allows an operation at a height within a predetermined range without contact of a finger with a panel surface (this proximity operation is called a hover operation). FIG. 22 illustrates the schematic configuration of the capacitive touch panel. In FIG. 22, transmission electrode 101 and reception electrode 102 are disposed on the undersurface of plate-like dielectric 100 so as to be spaced apart from each other, and a drive pulse is applied to transmission electrode 101 from drive buffer 103. An electric field is generated when the drive pulse is applied and, when a hand is put into the electric field, the number of electric flux lines between transmission electrode 101 and reception electrode 102 is reduced. This change in electric flux line is manifested as a change in electric charge in reception electrode 102. The approach of the hand to the touch panel is detected from the change in electric charge in reception electrode 102. FIG. 23 illustrates a detection state of a finger when the hand is gradually moved toward the touch panel. In FIG. 23, (a) illustrates a state when the hand is away from the electric field, (b) illustrates a finger hover detection state when the finger has entered the electric field, and (c) illustrates a finger touch detection state when the finger is completely in the electric field and touches the touch panel.
An example of the prior art of the capacitive touch panel includes a touch switch described in JP-A-2009-181232. The touch switch described in JP-A-2009-181232 has, in a touch panel as a touch operation part for an operator, a plurality of detection means for detecting the touch operation of the touch panel, and detects a touch operation position in the touch panel by monitoring a change in the detection values of the detection means and determining the position of the detection means of which the detection value is changed as the touch operation position. The touch switch includes a first touch operation determination means for determining the presence or absence of the touch operation by detecting whether or not the detection value exceeds a first threshold value as a determination criterion of the touch operation, and a second touch operation means that extracts the detection position as the touch operation position in the case where a characteristic value of the detection value has a high value when the detection value does not exceed the first threshold value but exceeds a second threshold value set to a value lower than the first threshold value, and does not extract the detection position as the touch operation position in the case where the characteristic value of the detection value has a low value.
Incidentally, in the capacitive touch panel, in the case where a hand is covered with a glove, the capacitive touch panel cannot differentiate between an operation with a finger covered with the glove and the hover state of a finger that is not covered with the glove. In addition, even when the touch panel is touched, the touch cannot be detected correspondingly to the thickness of the glove, and hence it is not possible to detect which part of the touch panel is pushed.
In order to detect a touch with a glove, it is possible to detect the touch with a glove by detecting a depression during the detection of a hover state. However, when an electronic device having the capacitive touch panel is held by a left hand and a display surface is touched with a gloved right hand, if the left hand is moved by the pushing force, there are cases where a force for pushing the display surface is lessened and the depression cannot be detected. In these cases, it is not possible to detect which part of the touch panel is pushed.
In addition, in the capacitive touch panel, in the case where the capacitive touch panel is operated with a nail, the capacitive touch panel cannot differentiate between the operation with the nail and the hover state of the finger. In particular, touch determination for the touch panel is performed in the case where a skin (conductive substance) having an area not less than a predetermined area comes in contact with the touch panel, and hence the touch determination is not performed when the touch panel is touched with a long nail or an artificial nail. Consequently, in this case as well, it is not possible to detect which part of the touch panel is pushed.